<!DOCTYPE html>
<html>
  <head>
    <script>

function tweak() {
  document.body.offsetTop;

  var feImage = document.getElementsByTagName("feImage")[0];
  feImage.setAttribute('filter', 'url(#f1)')
  document.body.offsetTop;

  var child = document.createElementNS('http://www.w3.org/2000/svg', 'g')
  feImage.appendChild(child);
}

    </script>
  </head>
  <body onload="tweak()">
    <svg xmlns="http://www.w3.org/2000/svg">
      <filter filterUnits="userSpaceOnUse" id="f1">
        <feImage/>
      </filter>
      <rect height="100" width="100"/>
    </svg>
  </body>
</html>
